Present day motor vehicle air conditioning systems include a heater core which draws heat from the radiator coolant of an internal combustion engine.
While suitable for their intended purpose, such heater cores do not provide instantaneous heat flow into the vehicle during winter operation. Additionally, they occupy additional space in a heating, ventilating and air conditioning (HVAC) module. The use of turbines driving a compressor for heating cabin air is known in aircraft heating systems.
Air cycle air conditioning or heating has not taken place in automobiles since high speed operation under idle conditions is not available in existing vehicles and especially in the case of internal combustion engine driven vehicles. Such prior vehicle power systems have included internal combustion engines with speed ranges from 600 rpm at engine idle conditions to 5,500 rpm during vehicle acceleration. In contrast, in the operation of turbocompressor driven aircraft air conditioning systems the components are operated in a speed range of from 30,000 to 100,000 rpm.
Air cycle refrigeration systems are used in aircraft cabin air conditioning systems. U.S. Pat. No. 4,262,495 discloses such a system wherein air is compressed in a manner to provide heated air to the aircraft cabin. The '495 patent discloses a system that draws stale air from the cabin; the air is filtered, compressed and cooled or heated in a recirculation loop. The patent does not suggest use of such air cycle cooling/heating in a system in which the power source is a high speed motive drive that receives its power from an internal combustion engine that powers an automobile. Further, there is no suggestion in the '495 patent of utilizing an air cycle heating mode to replace the heater core in the HVAC module of an automotive air conditioning system.
U.S. Pat. No. 4,665,715 discloses an air cycle cooling system proposed for use in automotive applications. It includes a drive shaft 35 for driving a compressor that compresses air that is then directed through a heat exchanger and a turboexpander 28 for cooling the air flow for use in an enclosure 30. There is no suggestion of providing a drive system that will efficiently operate the air cycle air conditioning system when an automobile is powered by a low speed internal combustion engine. Nor is there any suggestion in the '715 patent that hot compressed air from the compressor be used in a ventilating system to replace the ambient air heated by a heater core of a HVAC module in an automotive air conditioning system.
Applications of air cycle automotive air conditioning in which low speed operation are set forth in U.S. Pat. Nos. 3,686,893; 3,877,245; 3,884,664; 3,886,763; 3,886,764 and 3,886,765 by Thomas C. Edwards. The Brayton cycles shown therein have been tested by the assignee of the present invention. Test results show that the Edwards system has an inadequate air flow rate and too low an isentropic efficiency for use in commercially acceptable automotive air conditioning systems due to use of a low speed, e.g., 2500 RPM, rotary vane type compressor and expander.